FR2727106A1 - METHOD OF ENAMELLED GLASS SUBSTRATES, EMAIL COMPOSITION USED AND PRODUCTS OBTAINED - Google Patents

Abstract

The invention relates to an enamel composition for a glass substrate and its application. The enamel composition comprises a glass frit and pigments in a weight ratio between the frit and the pigments of between 65/35 and 30/70 per 100 parts of sintered mixture and pigments, with at least 10 parts of pigments which do not modify the chromaticity of the enamel layer.

Description

N 1994069 - SGV

  METHOD OF ENAMELLED GLASS SUBSTRATES, COMPOSITION

  EMAIL USED AND PRODUCTS OBTAINED.

  The present invention relates to a method for enamelling a glass substrate, especially a glazing unit, an enamel composition used in this process.

and the enamelled products obtained.

  Enamels for glass substrates are well known in the state of the art. They are used to form layers on glass substrates such as glazings, in particular curbs, decorative layers, protective layers, in particular UV protection layers for adhesive layers or adhesive cords intended for mounting windows in the body bays, or for the mounting of accessories, for example mirror holder, or

  as masks for collecting bands of heating networks, etc.

  The enamels used for these applications are generally employed in the form of an enamel composition comprising a powder consisting essentially of at least one glass frit (vitreous matrix) and of pigments as dyestuffs in particular, glass frit and glass frit. pigments being based on metal oxides, and a medium or "vehicle" for applying the enamel composition to the substrate and its temporary adhesion therewith. The medium chosen according to the destination of the enamel must ensure a good suspension of the used frit and pigment grains and must be burned during the cooking of the enamel. This medium can

  include solvents, thinners, oils, resins, etc ...

  In order to be able to fulfill its functions of mask and / or protection against UV radiation, an enamelled layer for glass glazing must have a certain opacity. This opacity can be expressed in terms of optical density. Thus, when it is an enameled layer intended to protect a bead, the desired opacity corresponds to an optical density of at least 3. The optical density is measured with a densitometer, for example the apparatus GRETAG RD 200. The optical density (OD) is related to the light transmission factor TL by the relation DO = log 1 / TL The opacity is obviously related to the thickness of the enamel layer and currently the enamel layers used industrially for coating glazing should generally have a thickness greater than about pm in the wet state, that is to say after the application of the layer on the substrate and before drying and firing, to ensure an optical density at less than 3. A wet thickness of 30 μm, which corresponds approximately to a thickness of 20 μm for the layer after firing, should be considered as important for an enamel layer. It therefore requires the use of a large amount of enamel and the cost

is high.

  On the other hand, when it comes to manufacturing a glazing with enamel areas of very different optical densities, one of the other, for example when it is a roof glazing automotive to present an enamelled central zone with a halftone pattern, and an enameled peripheral band of high optical density (OD> 3), it is generally necessary to achieve the enameling to use at least two passes for producing the enamel layer when it is desired to obtain a good definition of the raster pattern. In a first pass, the enamel layer is deposited at least in the central zone in the form of a thin layer having a very fine grid, for example with the aid of a first screening screen of a mesh. of 120 T which corresponds to 120 threads / cm and a mesh opening of approximately 45 pm, and in a second pass the thicker peripheral band is deposited by using a second screen printing cloth having, for example, a mesh of T which corresponds to a mesh aperture of about 92 pim. This process which uses at least two passes for the deposition of the enamel layer is long and therefore expensive because it requires two stations of

silkscreen and two drying.

  The invention obviates the disadvantages mentioned.

  It proposes an enamel composition which allows the manufacture of a very opaque layer under a small thickness while using the usual industrial manufacturing conditions, in particular by using temperatures

usual cooking.

  The enamel composition according to the invention comprises at least one glass frit and pigments, and this with a ratio by weight between the frit and the pigments of between 65/35 and 30/70 per 100 parts of sintered mixture and pigments with at least 10 parts of pigments that do not modify

  significantly the chromaticity of the enamel layer.

  The chromaticity can be characterized by the colorimetric coordinates designated by the letters a * and b *, these coordinates deriving from the X, Y and Z trichromatic coordinates defined and proposed in 1931 by the International Commission on Illumination (CIE), Commission unanimously recognized as a reference body for colorimetry. The coordinate system L *, a *, b * (L * characterizing luminance), commonly known as CIELAB, has been the subject of an official recommendation

  CIE in 1976 (International Commission on Illumination, Colorimetry-

  Official Recommendations - CIE Publication No. 15-2, Vienna, 1986) and is

  used in a large number of industrial sectors.

  According to the invention, at least 10 parts of the pigments with respect to 100 parts of the frit and the pigments do not alter or modify the values

a * and b * significantly.

  Compared with known enamel compositions for glass substrates, the composition according to the invention therefore contains a general content of pigments expressed with respect to the sinter-pigment mixture which is much higher than the usual contents. Below 35% of pigments with respect to the sintered mixture plus pigments, the improvement of the opacity is not very significant. Beyond 70% in pigments the composition does not lend itself to the usual conditions of cooking. Advantageously, the ratio by weight between the frit and the pigments is between 50/40 and 40/60, that is to say with a pigment content greater than 40 parts relative to the 100 sintered parts and pigments. This high content of pigments surprisingly improves the opacity of the enamel layers produced according to the invention, compared to the

  known layers of equal thickness.

  However, this high pigment content is only possible according to the invention if at least 10 parts of the pigments are pigments which do not alter

  significantly the chromaticity of the enamel layer.

  This improvement in opacity allows, under one aspect of the invention, the manufacture of enamel layers of lower thickness. As will be shown by the examples described hereinafter, it is possible according to the invention to reduce by half and more the thickness of the enamel layer while

  keeping opacity comparable to that of known layers.

  The enamel composition according to the invention can advantageously be prepared from existing enamel compositions or from components of existing enamel compositions, such as glass frits. The preparation can be done by adding pigments to the preceding compositions or components, so as to obtain the proportions indicated above between the frit and the pigments with at least 10 parts of pigments which do not affect the chromaticity. The invention does not necessarily imply a complete reformulation of the enamel compositions employed, nor does it imply any modifications of the

  implementation of traditional enamelling processes.

  The glass frit of the enamel composition may be any known glass frit based on oxides chosen, for example, from oxides of silicon, lead, zinc, bismuth, titanium, zirconium, sodium, boron, lithium, potassium, calcium, aluminum, tin, vanadium,

molybdenum, magnesium, etc ...

  The increase of the pigment content according to the invention with respect to a given enamel composition can influence the melting temperature of the

  enamel composition especially when it comes to very high levels of pigment.

  It may then be advantageous to choose frits with a lower melting point so as to find the usual melting temperatures and thus not to modify the industrial enamel cooking process. Thus, in one aspect of the invention, a frit with a melting point which is lower than the

Pigment rate is high.

  It should be noted that the large amount of pigments used according to the invention does not affect the resistance characteristics significantly.

  mechanics of the coated glass substrate.

  The medium present in the enamel composition according to the invention may be any medium usually used in known enamel compositions. It may include solvents, diluents, oils such as pine oils and other vegetable oils, resins such as resins

  acrylics, petroleum fractions, film-forming materials, etc.

  The pigments used according to the invention may be chosen from compounds containing metal oxides such as chromium oxides, copper oxides, iron oxides, colbalt oxides, nickel oxides. With regard to the pigments that do not change the chromaticity, we

  will choose in particular copper chromates, cobalt chromates, ...

  Advantageously, the enamel composition according to the invention comprises at least 5% and preferably at least 20% by weight of chromate of copper and / or cobalt, expressed with respect to the sintered weight plus pigment of the

composition.

  Preferably, the enamel composition contains at least 30% by weight

of copper chromate (spinel).

  According to one characteristic of the invention, pigments having a given particle size are chosen. Thus, advantageously, at least 50% of the pigments have a particle size greater than 2.5 μm. and with

  preferably an average particle size of between 3 and 5 μm.

  In the process of enamelling glass substrates, especially glazing according to the invention, the enamel composition is preferably deposited by screen printing on the substrates, and then fired, the firing taking place, if necessary, during the thermal treatment bonded to the substrate. bending and / or quenching of the substrates, the cooking temperatures being generally of the order of 600-

700 C.

  The deposition of the enamel composition can also be done by spraying,

  by curtain or roller coating, etc.

  The deposit is generally followed by drying.

  The enamel composition according to the invention allows the manufacture of

  enamel layers of high opacity compared to the thickness of the layer formed.

  Thus, the enamel layer may have an optical density greater than

  3 for thicknesses less than 15 μm (in the wet phase).

  This very good opacity ratio on the thickness of the layer makes it possible, in particular for certain enamelled glazing applications, to produce enamelled layers in a single pass, whereas it was necessary to use at least two passes with the known enamel compositions. For example in the case of a glazed glazing for automotive roof which must have different opacity values according to the areas of the glazing, namely a central zone of low opacity, for example of optical density equal to 1, generally formed of a thin layer having a weft, and a peripheral zone of high opacity, for example of optical density greater than 3, it is possible with the enamel composition according to the invention to operate the deposition of the enamel layer in a only pass corresponding to the deposition of a thin layer, this single pass nevertheless allowing obtaining an opacity for the zone

  device that meets the acceptance criteria.

  The very good opacity provided by the enamel composition according to the invention in the application as a peripheral band serving as a mask for the adhesive bead in a glazing unit makes it possible, if necessary, to eliminate the well-known treatment operation, consisting of in a coating by a black primer of the glazing area to receive the adhesive bead when mounting the glazing in the car body bay. In this case, a conventional thickness is preferably used, that is to say

  greater than 30 μm (when wet).

  The enamel composition according to the invention also makes it possible to obtain a very good definition of the patterns deposited by screen printing thanks to the use of thin-screen screen fabrics suitable for low thicknesses of

enamel layer.

  It allows a luminance drop without modifying the values a * and b *, that is to say that it allows to obtain an intense black color without

  appearance of particular chromaticity.

  In addition, the composition according to the invention provides an improvement of the surface appearance of the fired layer, with a low roughness, as well as an improvement of the anti-adhesive properties ("anti-stick") in particular vis-à-vis

  forming tools (tempering, bending) quite surprising.

  Other advantages and features of the invention will appear in

  the following description of examples of manufacturing glazed glazings using

  the enamel compositions according to the invention.

  EXAMPLE 1 In order to manufacture a tempered glass pane provided with a peripheral enamelled strip, a non-stick enamel composition (with respect to the forming tools) containing a glass frit based on PbO is used. , SiO2 at 65 parts and pigments especially based on Fe 2 O 3,

  Cr203, C0304, 34.5 parts per 100 parts sinter plus pigments.

  This composition is mixed with a medium in order to be deposited by

  silkscreen on a glass pane to form the enamelled peripheral band.

  The medium may be any known medium and in particular a medium based on a resin and a solvent or based on UV-polymerizable acrylic compound. A 35 μm thick layer is then deposited in the wet state using a After drying, the glazing is subjected to a heat treatment at 680 C. This heat treatment can be that related to the quenching process. The

  baking of the enamelled strip is performed during this heat treatment.

  The enamelled layer finally obtained has a thickness of about 20 microns. Using the GRETAG R D 200, the optical density is measured

  the glazed part of the glazing. The value is 3.5.

  Control Example 2 The procedure is the same as in Example 1, except that a 12.5 μm thick layer is deposited in the wet state using a protective cloth.

  mesh 120 T. The optical density finally obtained is 2.7.

Example 1

  To the enamel composition of Control Example 1 was added 10 parts of additional pigments per 100 sintered parts and pigments. The added pigment is copper chromate in spinel form. This pigment does not alter the original chromaticity of the enamel layer. The sinter / pigment ratio is

then 59.5 / 40.5.

  After addition of a medium, the enamel composition is deposited on the glaze by screen printing using a web 120 T to form a 12.5 μm thick layer. After baking, the optical density of the enamelled part of

Glazing is 3.3.

Example 2

  The procedure is as in Example 1 except that 20 parts of pigments (copper chromite) are added. The sinter / pigment ratio is then 54.6 / 45.4. An enamel layer 11 μm thick is formed. The density

optical obtained is 3.7.

  Compared to the control example 2, it can be noted that the addition of 20 parts of pigments made it possible to obtain a TL transmission approximately ten times

weaker.

  Control Example 3 In order to manufacture a laminated glazing unit provided with a peripheral enamelled strip, use is made of an enamel composition containing a glass frit and pigments in the following proportions expressed by weight PbO: 50.5 Cr203: 20.6 SiO2: 15.1 CuO: 9.4 TiO2: 1.5 Co304: 1.2 Na2O: 0.4 ZnO 0.4

AI203: 0.3

Fe203: 0.3

K20: 0.3

  The pigment content calculated on the basis of the metal oxides Cr 2 O 3, CuO, Co 3 O 4, Fe 2 O 3 is 31.5%. The sinter / pigments ratio is therefore

68.5 / 31.5.

  After mixing with a medium, the enamel composition is deposited by screen printing on a glass sheet to form an enamelled strip. A layer of enamel thickness of 35 μm in the wet state is thus deposited using a screen printing cloth 61 T. After drying, the sheet of glass coated with its printed layer is associated with a second sheet of glass. The assembly is then brought to a gravity bending furnace. During the thermal cycle related to the bending

  the cooking of the enamel is done at about 600 C.

  The optical density measured on the enamelled part of glass sheet is

3.4.

  Control Example 4 The procedure is as in Control Example 3 except that the thickness of the enamel layer is reduced to 25 μm using a 120 T.

  The measured optical density is 2.4.

Example 3

  To the enamel composition of Control Example 3 was added 10 parts by weight of pigment. The pigment used is copper chromate whose granulometry is such that 50% of the grains have a diameter greater than 3 μm. The sintered ratio on pigment is 62/38. This pigment does not affect the

  chromaticity of the enamel layer.

  The procedure is then as in Control Example 4, using a 120 T screen printing screen to form a 24 μm enamel layer.

  thick. After heat treatment, the optical density is 3.2.

Example 4

  The procedure is as in Example 3 except that 18 parts of pigments (copper chromate) are added to the starting composition. The report

  sinter / pigments is then 57.8 / 42.2.

  With this composition and after mixing with a medium, an enamelled strip of 24 μm in thickness is formed. After heat treatment, the

optical density is 3.4.

EXAMPLE 5

  50 parts of a frit made from Pb304 and PbSiO3, with a low melting point (about 480.degree. C.) are mixed with 50 parts of pigments, essentially

copper chromate.

  This composition has a melting point of about 680 C. With the aid of a screen printing screen 120 T, an enamel layer is formed which, after

  680 C has a thickness of 10 μm. The optical density is 4.5.

  The preceding examples show the good characteristics, especially in opacity, of the enamel compositions according to the invention which contain a higher pigment content than the known compositions, and with at least 10 parts of pigments which do not alter

  not the chromaticity of the enamel layer.

Claims (11)

  An enamel composition for a glass substrate comprising a glass frit and pigments, characterized in that the weight ratio of the sinter and the pigments is between 65/35 and 30/70 per 100 parts of sintered mixture and pigments , with at least 10 parts of pigments that do not   do not change the chromaticity of the enamel layer.   2. enamel composition according to claim 1, characterized in that   the ratio between the frit and the pigments is between 60/40 and 40/60.   3. enamel composition according to one of claims 1 or 2,   characterized in that it contains at least 5% and preferably at least 20% by weight of copper chromate and / or cobalt as a pigment which do not affect the chromaticity.   4. enamel composition according to claim 3, characterized in that   it contains at least 30% by weight of copper chromate.   Enamel composition according to one of Claims 1 to 4, characterized   in that at least 50% of the pigments have a particle size greater than 2.5 μm.   Enamel composition according to one of claims 1 to 5, characterized   in that the frit is a low melting point frit.   7. Process for the enameling of a glass substrate, in particular a glazing unit, in which at least a part of the glass substrate is coated with   enamel composition according to one of claims 1 to 6 and subjecting the   enamelled substrate to a heat treatment ensuring the enamel cooking.   8. Method according to claim 7, characterized in that the layer of   coating is formed by screen printing.   9. Enamelled glass substrate obtained by the implementation of the process   according to one of claims 7 to 8.   10. enamelled glass substrate according to claim 9, characterized in that it has an optical density greater than 3 for an enamelled layer   Thickness less than 15 μm (wet).   11. enamelled glass substrate according to claim 9, characterized in that it has at least one enamelled area with an optical density greater than 3 and at least one enamelled high-resolution enamelled area and these different   enamelled areas are obtained in one pass.